This invention relates in general to low physical profile antennas and, in particular, to a dual band microstrip antenna employing a single coplanar feedline and a dual band microstrip radiating element.
A common dual-band (or multiple-band) design of microstrip antennas employs an antenna structure in which single-band microstrip radiating elements are stacked above a ground plane with the surface of each element dimensioned so as to resonate at a different frequency. Each of the radiating elements is fed with a separate feedline, either a coplanar feedline or a coaxial-to-microstrip adapter normal to the plane of the radiating element. The multiple layers and the multiple feedlines result in a less compact and more complex structure than is desirable for some aerospace applications.
Dual band operation using microstrip antennas and feed networks etched on the same surface have been constructed. U.S. Pat. No. 4,356,492 discloses a dual band antenna in which two single-band coplanar radiating elements are fed from a common coplanar input point.
Instantaneous dual band operation using single element microstrip antennas and feednetworks etched on the same surface require either (1) microstrip antennas with a single feedline on the same surface as the antenna (coplanar antenna) or (2) diplexed output ports on the feed network. Dual band, coplanar, single feedline antenna designs are available only if the frequencies of interest are within 15 percent of each other or are harmonically related. Diplexers in the feed network result in a larger, less efficient, and more complex microstrip antenna array.